16.12. The MAC Biba Module

Module name: mac_biba.ko

Kernel configuration line: options MAC_BIBA

Boot option: mac_biba_load="YES"

The mac_biba(4) module loads the MAC Biba policy. This policy works much like that of the MLS policy with the exception that the rules for information flow are slightly reversed. This is said to prevent the downward flow of sensitive information whereas the MLS policy prevents the upward flow of sensitive information; thus, much of this section can apply to both policies.

In Biba environments, an integrity label is set on each subject or object. These labels are made up of hierarchal grades, and non-hierarchal components. As an object's or subject's grade ascends, so does its integrity.

Supported labels are biba/low, biba/equal, and biba/high; as explained below:

Biba provides for:

The following sysctl tunables can be used to manipulate the Biba policy.

To access the Biba policy setting on system objects, use the setfmac and getfmac commands:

# setfmac biba/low test
# getfmac test
test: biba/low

Observations: a lower integrity subject is unable to write to a higher integrity subject; a higher integrity subject cannot observe or read a lower integrity object.

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